For those interested, Alexander Samely has put together a fantastic collection of his comments on all of the Old Testament quotes (and allusions)in the Mishnah (except for those quotes found in tractate Aboth). The database can be searched by tractate or by OT reference.
This a great resource for anyone interested in studying the use of the Old Testament by early Jewish and Christian writers!
Take a look:
Database of Midrashic Units in the Mishnah